1. Field of the Invention
The present invention relates to a power controlling method of an optical disc drive, and more particularly, to a power controlling method capable of removing an output power shift outputted by a pickup head of an optical disc drive.
2. Description of the Prior Art
For a company or a human, it is important to manage or store a document. In the past, because most documents are printed or written of otherwise paper-based, if a number of the documents is huge, the documents are inconvenient to users because of their weights and volumes. Recently, as computer technology progresses, digital data is widely utilized and stored in a computer storage medium. Many types of data storage devices have been invented to assist users by simplifying digital data storage. For example, the compact disc recorder was invented. The above-mentioned compact disc recorder, such as a CD-R drive or a CD-RW drive, can store data into a CD-R disc or a CD-RW disc. Because the optical disc has the advantages of low cost, small volume, and big capacity, the users can preserve data more easily. Before writing data into a CD-R disc, the CD-R drive must perform an optimum power control (OPC) procedure to find out an optimum recording power of the CD-R disc. Furthermore, the compact disc recorder performs a burning operation on the CD-R disc according to the optimum recording power to form corresponding pits to store binary data “0”. And the other flat area is utilized to store binary data “1”. For the above-mentioned CD-RW disc drive, the above-mentioned optimum recording power can be utilized as an erase power of the CD-RW disc drive, where the erase power is utilized to reform a CD-RW disc to re-uniform the surface of a recording layer of the CD-RW disc to be flat.
Please refer to FIG. 1, which is a block diagram of a power controlling system 10 of a CD-R disc drive according to the prior art. The power controlling system 10 encompasses a controller 12, a power control unit 14, a pickup head 16, and a transformer 18. The controller 12 is utilized to control operations of the power controlling system 10. The power control unit 14 is utilized to adjust an output power of the pickup head 16 to write data into a CD-R disc, where the power control unit 14 includes a sample/hold circuit 20, a digital-to-analog converter (DAC) 22, and a driving circuit 24. The sample/hold circuit 20 is utilized to control the pickup head 16 and the power control unit 14 as a close loop or an open loop. The DAC 22 is utilized to transform a digital control signal 26 to an analog control voltage 28. The driving circuit 24 then outputs a control voltage 30 according to the control voltage 28 in order to drive the pickup head 16 to generate a laser having a predetermined power. Therefore, the pickup head 16 can adjust its output power according to the control voltage 30 generated by the power control unit 14. Furthermore, when the pickup head 16 writes data into the CD-R disc, the variation of the output power of the pickup head 16 is detected. Furthermore, the pickup head 16 of the power controlling system 10 emits an incident pulse to etch the optical disc. The incident pulse is then reflected by the optical disc to form a reflected pulse. The reflected pulse has a reflected pulse level (also called as B-level in the specification) to represent the etching degree of the optical disc. Next, the transformer 18 generates a corresponding feedback signal 32 to the power control unit 14 according to the reflected pulse level (here, the reflected pulse level can correspond to the current output power of the pickup head 16) in order to further adjust the output power of the pickup head 16. If the control signal 26 corresponds to the optimum recording power then the output power of the pickup head 16 can be adjusted to be close to the optimum recording power through the control of the close-loop of the pickup head 16 and the power control unit 14. At this point, the optimum recording power can be outputted through the pickup head 16 in a stable fashion.
The operation of the power control system 10 of the CD-R disc drive is illustrated as follows. The pickup head 16 can emit lasers to etch the recording layer of the optical disc in order to store data. The characteristics of different optical discs may be different. For example, the recording layers of different types of optical discs may be different because of the materials utilized in their manufacture. In other words, the recording layers of different types of the optical discs may have different absorbing layer characteristics. Therefore, it is not sufficient to simply emit the same power to different optical disc. Emitting the same power may result in unwanted variations of the etching degrees. As mentioned above, when producers manufacture optical discs, the producers will store a needed recording power of a specific optical disc in a lead-in area of the specific optical disc. Furthermore, the power controlling system 10 often utilizes an optimum power control (OPC) process to obtain the recording power P1 of the optical disc. Once the power controlling system 10 has obtained the recording power P1, the recording power P1 can be utilized to record data in the recording layer of the optical disc. The power controlling system 10 simultaneously obtains the corresponding relationships between the output power of the pickup head 16 and the control signal 26, according to the specifications of the digital-to-analog converter 22 and the pickup head 16. For example, when the control signal 26 is DAC1 (this also means that the control voltage 28 is the voltage V1), the ideal output power of the pickup head 16 is P1, however, the real output power of the pickup head is P2. The output power P2 is transformed by the transformer 18 to generate the feedback signal 32 corresponding to a voltage V2. Because the pickup head 16 must etch the optical disc to store data (in order to store the binary data “0”), the controller 12 turns on the sample/hold circuit 20 to cause the pickup head 16 and the power control unit 14 to form a close loop. Because the voltage V2 of the feedback signal 32 is not the same as the voltage V1 of the control voltage 28, the driving circuit 24 adjusts the control voltage 30 according to the voltages V1 and V2 until the voltages of the feedback signal 32 and the control voltage 28 are the same. Therefore, the pickup head 16 can etch the optical disc by outputting, in a stable fashion, the power P1. Therefore, every time the output power of the pickup head 16 is not stable and far from the output power P1, the close loop of the power control unit 14 and the pickup head 16 can adjust the output power of the pickup head 16 through the driving circuit to make the output power return the needed optimum recording power P1. As a result, the data writing operation can be performed correctly.
However, in the actual circuit, because the sample/hold circuit 20 encompasses capacitors and/or other different electronic devices, the sample/hold circuit 20 influences the input signal. In an ideal situation, when the sample/hold circuit 20 is turned on to cause the pickup head 16 and the power control unit to form a close loop, the sample/hold circuit 20 can be utilized to hold the feedback signal 32 inputted by the transformer 18. Unfortunately, in the actual operation of writing data, the sample/hold circuit 20 performs corresponding on/off operations according to the write-in data. The outputted signal will be affected because the sample/hold circuit 20 is self-influenced by its own operation. In other words, the feedback signal 32 outputted by the sample/hold circuit 20 may vary from the normal. The result is a shift in the output power of the pickup head 16 due to this variation in the feedback signal 32 inputted into the driving circuit 24.
Please refer to FIG. 2 and FIG. 3. FIG. 2 is a diagram of the output power of the pickup head 16 shown in FIG. 1. FIG. 3 is an operational timing diagram of sample/hold circuit 20 shown in FIG. 1. Assume that the CD-R disc drive 10 must output lasers having the power P1 to etch an optical disc to store the binary data “0” in time T1, T2, T3, and T4. The CD-R disc drive 10 must utilize the recording power P1 to etch an optical disc to store a binary data “0”. This operation requires that in time T1, T2, T3, and T4, the sample/hold circuit 20 also be simultaneously turned on such that the pickup head 16 and the power control unit 14 can form a close loop to regulate the output power of the pickup head. However, because the sample/hold circuit 20 comprises capacitors or other electronic devices, frequently turning the sample/hold circuit 20 on and off will result in the above-mentioned operation wrongly influencing the actual output signal of the sample/hold circuit. The result is that the feedback signal 32 inputted into the driving circuit 24 shifts and then influences the output power of the pickup head 16 to move away from the predetermined power P1. For example, assume that the sample/hold circuit 20 is always turned on instead of being turned on and off frequently. Also, assume that the value of the input control signal 26 is 10 and the control signal 26 can drive the pickup head 16 to stably output lasers having a power 50 mW. Furthermore, when executing an actual data storing operation, if the CD-R disc drive 10 inputs a control signal 26 of value is 100 into the DAC 22, the control signal 26 is transformed into the corresponding control voltage 28, whose voltage is V1. However, when the pickup head 16 starts to operate, the pickup head 16 may only output lasers having the power 45 mW because of its characteristics. Therefore, when the pickup head 16 detects the pulse signals reflected from the optical disc, the pulse signals can be transformed into a feedback signal 32, whose voltage value is V2, through the transformer 18.
When the feedback signal 32 is inputted into the sample/hold circuit 20 and utilized to adjust the output power of the pickup head 16 through the above-mentioned close loop, the sample/hold circuit 20 makes the feedback signal 32 shift to voltage V1 instead of the original voltage V2 because the sample/hold circuit 20 is turned on and off frequently. With respect to the driving circuit 24, the output power of the pickup head 16 is not adjusted through the driving circuit 24 because the outputs of the sample/hold circuit 20 and the DAC 22 are the same. Therefore, the pickup head 16 stably outputs lasers having 45 mW power instead of the required output power 50 mW. Apparently, because of the influence of the sample/hold circuit 20, an offset Δp between the predetermined output power P1 and actual output power P2 of the pickup head 16 is generated (of course, according to the circuit characteristic of the sample/hold circuit 20, the actual output power P2 of the pickup head 16 may be greater than the predetermined power P1). In the actual operation of writing data, the CD-R disc drive 10 can utilize the control signal corresponding to the optimum power, generated through the OPC procedure, to drive the pickup head 16. Unfortunately, the sample/hold circuit 20 causes the actual power of the pickup head 16 to shift from the optimum power; the etching degree of the optical disc and the stored data are both negatively influenced. Therefore, when the optical disc is utilized to read stored data, the data may be read incorrectly because of the incorrect etching degree.
For a prior art CD-RW disc drive, the CD-RW disc drive can be utilized to perform a data writing and a data erasing operation on a CD-RW disc. The pickup head of the CD-RW disc drive needs a writing power to etch the optical disc to generate holes on the optical disc. Furthermore, it needs an erasing power to remove the data on the optical disc (that is, the erasing power is utilized to reform the recording layer of the optical disc in order to re-uniform the surface of the optical disc so that the data can be removed). As known by those skilled in the art, the operation and the structure of the CD-RW disc drive when outputting the erasing power is the same as the operation and the structure of the CD-R disc drive 10. In other words, the erasing power is stabilized through a close loop. That is, the erasing power is utilized to form a land on the optical disc. In addition, the CD-RW disc drive turns on the sample/hold circuit to form the close loop. Therefore, like the CD-R disc drive 10, the CD-RW disc drive utilizes the control signal corresponding to the predetermined erasing power; however, because the sample/hold circuit 20 may shift the output power of the pickup head, the data writing operation is also negatively influenced.